Procedure of attaching sheets and padded envelope

ABSTRACT

The envelope comprises layers of plain un-coated kraft paper and of bubble-wrap polyethylene. A stack of the layers is joined at the marginal edges of the envelope by squeezing the stack between a pair of points-dies, which are formed with points that puncture the kraft paper but do not puncture the polyethylene. The points push crowns of un-punctured polyethylene through the punctured boles in the paper. Then, the marginal edges are squeezed flat between flat-dies, the flat-dies being heated enough to cause fuse-bonding. The margins of the finished envelope are held together not only by fuse-bonding, but by the presence of the crowns, which, penetrating right through the holes in the paper, serve as mechanical rivets.

This application is a 371 of PCT/CA02/01731, filed on Nov. 06, 2002.

This invention relates to padded envelopes, being envelopes that have anouter covering of paper, and an inner lining of plastic bubble material.Plastic bubble-wrap is a well-known, widely-used, packaging material,and comprises a flat-layer of a thin plastic, such as polyethylene(polythene), and a bubble-layer of thin plastic, which is partiallylaminated to, and partially separated from, the flat-layer. The areas ofseparation of the layers are isolated from each other, being completelysurrounded by the laminated areas, to form the bubbles.

BACKGROUND TO THE INVENTION

In bubble envelopes, the flat-layer of the bubble material forms theinside lining of the envelope, and is contacted directly by items placedin the envelope, and the paper (usually, kraft paper) forms the outsideof the envelope.

With the traditional bubble padded envelopes, a problem can ariseregarding recycling of the envelopes, and regarding the re-use of thematerials from which the envelopes are made. The problem has been that,if the bubble material was adhered to the paper strongly enough toprovide a serviceably-robust structure, it was not possible tophysically separate the bubble material from the paper, so that thedifferent materials could be recycled.

Proposals have been made to attach the bubble material to the paper insuch a way as to permit separation for re-cycling, but these proposalshave been very expensive, or not mechanically satisfactory, or haveinvolved the use of applied adhesives, which require the use ofsophisticated handling and positioning machinery.

The invention is aimed at providing a bubble padded envelope, in whichthe bubble material is attached to the paper in a manner that issatisfactory from the service or usage standpoint, and which permits thebubble material to be readily separated from the paper, for recycling.

It is also an aim of the invention to provide a manner of making apadded envelope, which provides a serviceably robust envelope structure,by a simple manufacturing procedure that requires a minimum of costlypreparation of the envelope components.

THE INVENTION IN RELATION TO THE PRIOR ART

An example of a prior design of bubble-padded envelope is shown inpatent publication U.S. Pat. No. 6,139,188 (Marzano, 2000)

In one traditional design of bubble envelope, the paper and the bubblematerial were first attached face to face over the whole area of thebubble material. In order to enable the polyethylene bubbles to stick tothe paper, the paper had to be itself coated with a thin layer ofpolyethylene, over its whole surface. Then, as a preliminary productionstep in the manufacture of the envelopes, the bubble material was placedagainst the coated side of the paper, bubble-tips touching the paper,under conditions of heat and (slight) pressure, whereby the tips of thebubble became attached to the paper. In this traditional manufacturingsystem, only when the paper had been coated, and the bubble materialthen stuck face-to-face over the coated paper, could manufacture of theenvelopes be commenced.

Envelopes manufactured by this traditional system, however, though veryrobust and serviceable, could not be recycled because the polyethylenecannot later be separated from the paper. Also, this system involvedimpregnating a coating of polyethylene into the kraft paper, prior tomaking the envelopes, which generally was carried out in a separatefactory from the manufacture of the envelope, and that could sometimeslead to inventory inefficiencies, etc.

It should be understood that, in the above-described traditional system,the securement of the bubble material to the coated paper, to form alayered composite, occurs over the whole interface between bubbles andpaper. That is to say, the tip of every bubble adheres to the paper. Itis not practical for the bubbles to be adhered to the paper over only anarrow band. The system provides that the bubble tips are secured veryfirmly to the pre-coated paper, but the disadvantage is that the bubblematerial cannot later be removed from the paper for recycling.

It may be noted that polyethylene cannot be reliably bonded to un-coatedpaper, simply by squeezing the polyethylene against the paper betweenheated dies. The polyethylene will bond a little, but not enough to besuitable for the manufacture of envelopes. Rather, the paper first hasto undergo the pre-coating process, which leaves a thin film ofpolyethylene on the paper, in which case the polyethylene bubbles adhereto the paper such that the two materials cannot later be separated.

It is also known, for example from DE-4,343,798, to provide an additiveto be included in the bubble material, which can be activated to causethe bubbles to adhere to the paper. Thus, the bubble material may beattached to un-coated paper, and this can be done by activating theadditive over pre-determined narrow bands. This allows the bubblematerial to be attached to the paper over only the outer margins thatmake up the envelope. The bubbles are not attached to the paper over themajority of the surfaces that comprise the envelope. This system canproduce satisfactory results, in that the envelopes are serviceable, yetthe envelopes can be torn apart, after use, and the paper and bubblematerial separated for recycling. However, the system is expensive, andprone to manufacturing difficulties.

The invention is also aimed at providing an envelope in which the bubblematerial is attached to the paper only at the edges or margins of theenvelope. Thus, again, the bubble material may be separated from thepaper for recycling after use. But the invention provides a manner ofattaching the bubble material to the paper in such a manner that nopre-coating of the paper is needed, nor adhesives, nor other items thatcan lead to production difficulties.

The invention is aimed at providing a manner of attaching the bubblematerial to the paper in a manner that is predominantly a mechanicalinteraction between the paper and the bubble material, rather than achemical adhesive interaction. In the invention, the aim is to enablepadded envelopes to be made using, as starting materials, a roll ofinexpensive plain un-coated paper and a roll of plain bubble material,and to attach the two materials to form an envelope configuration, by asimple clean production process. It is an aim of the invention that noadhesives or additives be required.

GENERAL FEATURES OF THE INVENTION

In one aspect, the invention lies in a procedure, as claimed, forjoining a sheet of paper to a sheet of plastic bubble-wrap material.More particularly, the invention lies in a procedure, as claimed, formanufacturing a padded envelope. In another aspect, the invention liesin an envelope that has been manufactured by that procedure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

By way of further explanation of the invention, exemplary embodiments ofthe invention will now be described with reference to the accompanyingdrawings, in which:

FIG. 1 is a pictorial view of a padded envelope that embodies theinvention.

FIG. 1 a is a sectioned side-elevation of the envelope of FIG. 1.

FIG. 2 is a diagram of production apparatus used for manufacturing theenvelope of FIG. 1.

FIG. 3 is a cross-sectioned end-elevation in the direction of arrows 3—3of FIG. 2.

FIG. 4 is a plan view of a stack of layers as it passes through theapparatus of FIG. 2.

FIG. 5 is an elevation showing a stack of layers and showing a pair ofpoints-dies of the apparatus of FIG. 2, prior to the points-dies beingbrought together onto the stack.

FIG. 6 a is a pictorial view of one of the points-dies of the apparatusof FIG. 2.

FIG. 6 b is a pictorial view like that of FIG. 6 a, but showing adiagonal arrangement of points.

FIG. 7 is a close-up showing a portion of the stack, as squeezed betweenthe points-dies.

FIG. 8 is the same close-up as FIG. 7, but after the points-dies havebeen withdrawn from the stack.

FIG. 9 is a close up of the same portion as FIGS. 7 and 8, but after thestack has been squashed flat by flat-dies of the apparatus of FIG. 2.

FIG. 10 is an elevation showing an alternative construction of thepoints-dies.

FIG. 11 is a corresponding elevation showing another alternativeconstruction of the points-dies.

FIG. 12 a is a diagram illustrating a slack-take-up position of thedies.

FIG. 12 b is a diagram illustrating a closed-together position of thedies.

FIG. 13 is a diagram illustrating a layout of points.

The apparatuses and procedures shown in the accompanying drawings anddescribed below are examples which embody the invention. It should benoted that the scope of the invention is defined by the accompanyingclaims, and not necessarily by specific features of exemplaryembodiments.

The padded envelope 20 of FIGS. 1 and 1 a comprises a top T and a bottomB, which are secured along their marginal far edge 24, and along theirmarginal left and right side edges 25L,25R, to create a pocket 26. Thetop T comprises an outer layer 27T of kraft paper 27, and an inner layer29T of polyethylene bubble-wrap material 29. The bottom B similarlycomprises an outer layer 27B of the kraft paper 27, and an inner layer29B of the polyethylene bubble material 29.

Typically, the kraft paper is about a hundred microns thick, and thepolyethylene film from which the bubble-wrap material is made is aboutfifty microns thick. Typically, the bubbles have a diameter of eight mm,are spaced on a hexagonal grid with a ten mm centre-to-centre distance,and the bubbles stand four mm high.

At the mouth of the pocket 26, the bubble layer 29T is adhered to thepaper layer 27T, and the bubble layer 29B is adhered to the paper layer27B, whereby the mouth 30 of the pocket comprises an opening between thetop bubble-layer 29T and the bottom bubble-layer 29B.

Some of the stages in the manufacture of the envelope are illustrated inFIG. 2. The manufacturing apparatus 31 includes a first station 32 (seealso FIG. 3), at which the left and right edges of the top layer 27T ofpaper are hot-pressed onto the left and right edges of the top layer 29Tof bubble, using heated dies 33LT,33RT, whereby the bubbles 35 aresquashed flat, and the polyethylene adheres to the paper, to form bondedmargins 34LT,34RT. Also, the left and right edges of the bottom layer27B of paper are hot-pressed onto the bottom layer 29B bubble, usingheated dies 33LB,33RB, whereby the bubbles of the bottom layer 29B aresquashed flat, and the polyethylene adheres to the paper, to form bondedmargins 34LB,34RB.

These margins 34LT,34RT,34LB,34RB will later form the lips of the mouth30 of the pocket 26. Again, it should be noted that the security levelof the kind of adherence that arises from simply hot-pressingpolyethylene onto un-coated paper is not very high, but in fact theadherence only needs to be adequate for the task of keeping the mouth ofthe pocket open, and hot-pressing onto un-coated paper is enough forthat.

The top layers 27T,29T are kept separate from the bottom layers 27B,29B,while being processed in the first station 32. The two top layers emergefrom the first station joined at the marginal edges 34LT,34RT but notjoined over the rest of the area of the layers. Similarly, the twobottom layers move forward to the second station, joined just at themarginal edges 34LB,34RB. The two top layers 27T,29T and the two bottomlayers 27B,29B advance separately to the second station 36.

At the second station 36, the top layers 27T,29T of paper and bubble arejoined to the bottom layers 27B,29B of paper and bubble, the areas ofthe joints being arranged in bands, which will later correspond to themarginal edges of the manufactured envelopes. FIG. 4 shows theconfiguration of the joint-bands 37 in plan view.

FIG. 5 is a view showing the stack 38 of layers, comprising top paper27T—top bubble 29T—bottom bubble 29B—bottom paper 27B. Also shown is apair of dies 39T,39B. Both dies are formed with points 40. FIG. 6 a is apictorial view of one of the points-dies 39B.

When the points-dies are brought together, the stack 38 of layers istrapped therebetween. As the dies come together, the bubbles 35 locatedbetween the dies are squashed flat. The portion of the stack trappedbetween the points-dies is then forced to follow the contours of thepoints 40.

It is a characteristic of paper, including the kraft paper 27 from whichpadded envelopes are made, that when a point is pressed into a sheet ofpaper, the paper can stretch resiliently to only a very limited extent.The paper will easily tear, i.e will be punctured, if a sharp point ispressed into the paper. Paper can stretch resiliently to only a limitedextent. Paper does have a yield point, in that, if slightlyover-stressed, paper will take a permanent set, without tearing. But itdoes not take much extra stress, beyond that, for paper to tear.

Polyethylene, including the polyethylene from which bubble material 29is made, on the other hand, has a much larger capacity than paper, whenover-stressed, to yield, and to carry on yielding, without puncturing.

It is recognised that, when a point is pressed into the stack 38 oflayers of paper and polyethylene, the effect is that the paper layersbecome punctured; the polyethylene layers yield, and become stretched,but the polyethylene is not punctured. It is recognised that each point40, if configured properly, can be arranged to push a crown ofun-punctured polyethylene right through the hole the point has puncturedin the paper.

In the condition as illustrated in FIG. 7, the points 40 on thepoints-dies 39T,39B have punctured holes right through the top andbottom layers 27T,27B of paper. The points have stretched the top andbottom layers 29T,29B of polyethylene beyond yielding, but have notpunctured the polyethylene.

FIG. 8 illustrates the condition of the stack when the points-dies39T,39B are withdrawn. A small crown 42 of over-stretched polyethyleneprotrudes through the paper. If the FIG. 8 stack is held up to thelight, points of light should be seen through the stack, indicating thatthe paper has been punctured; but, to repeat, only the paper has beenpunctured, not the polyethylene.

The stack 38 is now transferred to the third station 43 (FIG. 2). Inthis station, the stack is pressed between two flat-dies 45T,45B. Thesedies simply squash the FIG. 8 stack flat. The crowns 42 are compressed,from the outside of the paper, down onto the paper. Thus the crownsserve as mechanical rivets, holding the paper firmly secured to thepolyethylene. Now, the condition of the squashed stack is as illustratedin FIG. 9.

The flat-dies 45T,45B are supplied with heat, and apply heat to thepolyethylene, to the extent that the polyethylene is heated beyond itsthermoplastic limit. When it cools, the polyethylene acquires the FIG. 9shape permanently. As a result, the stack of paper and polyethylenelayers is held together securely, by a combination of fuse-bonding andmechanical interaction.

At the cutting station, or fourth station 46, the envelopes are finishedby cutting out, along the cut-lines 49 as indicated in FIG. 4. Also,strips 47 of press-to-stick adhesive are applied to the flaps 48.

The points 40 on the points-dies 39T,39B, as shown in FIG. 6 a, comprisepyramids 50, which are relatively easy to manufacture, being formed bygrinding grooves in a solid slab of metal. The pyramids are pitched on asquare grid, at around two or three millimetres apart. The tips of thepyramids are sharp, as are the four side edges of the pyramids.

Alternatively, as shown in FIG. 10, the points-dies 52T,52B may includeneedles. The needles 53 are manufactured separately from the slab 54 ofthe die, and pressed into sockets 56 therein. The needles 53 again forma square grid, pitched at around two or three mm apart. The tips 57 ofthe individual needles preferably are not sharp, but have a radius of ½or ¼ mm. A very sharp point on the tip 57 might lead to the unwantedpuncture of the polyethylene, whereas the radiused tip can stretch thepolyethylene as much as ten mm before puncture. On the other hand, theradiused tip is almost the equal of a sharp tip when it comes topuncturing the paper.

It may be noted that, in regard to the pyramids-style points-dies39T,39B of FIG. 6 a, the pyramids of the top die 39T are an exact fit tothe pyramids of the bottom die 39B. Thus, when the points-dies 39T,39Bare brought together, the whole surface area of the stack 38 is squeezedand compressed between the dies. That is to say, as the points 40 of thepyramids penetrate the paper, and drive the crowns 42 of polyethylenethrough the holes in the paper, the rest of the stack of layers aroundthe points is squashed flat.

As shown in FIG. 6 b, the points may alternatively be arranged indiagonal rows.

But it is not essential that the area of the stack around the points besquashed flat by the points-dies, as happens with the pyramids-style ofpoints-die, since the flat-dies 45T,45B will squeeze the stack flat. Theneedles-style of points-die 52T,52B leaves the area of the materialsimmediately surrounding the points un-compressed, which can be anadvantage in that the polyethylene can then the more easily flow intothe crowns without being over-stretched. Various configurations arecontemplated, of sharp points or rounded points, of a one-piece die orneedles let into sockets, of relief around the points or the diesclosing together over the whole are, and the like. The cost of makingthe dies is one factor, and the quality of the finished envelopes isanother.

The use of the needles-style of points-die 52T,52B may be expected tocreate larger crowns, i.e larger buttons of polyethylene that have beenpunched right through the paper to the other side of the paper, than thepyramids-style of points-die 39T,39B. Again, in FIG. 10, the stack oflayers is squeezed flat between heated flat-dies 45T,45B, after thestack has been separated from the points-dies.

It is essential that the points puncture right through the paper, but itis not essential that half the points penetrate through from one side,and half from the other side, in the symmetrically alternating up/downmanner as illustrated in FIG. 7. All the punctures may be from one side,if the designer wishes to arrange the dies that way. A needles-typepoints-die, in which the needles press only from one side, is shown inFIG. 11.

The punctures through the paper must be in the form of small points,each of which is surrounded by un-ruptured paper. It would not beacceptable for the paper to be punctured along a continuous line, forinstance, because that would mechanically weaken the material.Similarly, the punctured points should not, in the finished envelope,form a line of perforations, whereby the envelope might easily be tornalong that line.

If just one, or a few, of the points were to puncture, i.e make a holeright through, the polyethylene, that would not matter in itself;however, generally, for the security of the envelope, the polyethyleneshould not be punctured, and the presence of even one puncture mightindicate that an inadequate margin of tolerance had been provided.

The dies 45T,45B;39T,39B;52T,52B as depicted herein have been in theform of flat slabs. In use, the stack 38 of layers is advanced throughand between the dies, and then the movement of the stack is halted, andthe dies are brought together and pressed onto the now-stationary stack.After the dies are separated, the stack is then advanced to the nextstation. The cycle time for drawing the stack forward is dictated by thelength of time it takes to ensure that the polyethylene reaches itsthermoplastic temperature, in the flat-dies station (i.e the thirdstation 43).

The points-dies 39T,39B;52T,52B may be heated (in the second station36). This enables the overall cycle-time to be reduced, in that the timethe stack must spend between the flat-dies 45T,45B (in the third station43) can be reduced, since the materials in the stack are pre-heatedbefore reaching the third station.

Rather than being in the form of flat slabs, the dies may be in the formof rollers. In that case, the stack may be passed through the rollerswithout the cyclic stopping that is required when the dies are flatslabs. It may be noted that the term “flat” in the flat-dies refers tothe effect of the dies in squashing the stack flat, not in the shape ofthe dies. Thus, the flat-dies may actually be rollers.

Similarly, the flat-dies may have the effect of impressing the wholearea of the margin with, for example, an overall rounded-corrugated form(e.g corrugated in the view of FIG. 9), and still have the effect ofsquashing the crowns flat onto the outside surfaces of the paper, asrequired in the invention.

As shown, the far end 24 of the envelope 20 is made in the same manneras the side-edges 25L,25R, i.e by squeeze-bonding the joint-bands 37.The joint-bands 37 should be about two cm wide, whereby the bondedmargin at the edges 24,25L,25R of the finished envelope each have awidth of about one cm, when the envelopes are cut or stamped out, at thefourth station 46, along the cut-lines 49.

Alternatively, the designer may prefer to form the far edge 24, not bysqueeze-bonding, but simply by folding the layers over, whereby the topand bottom layers 27T,27B of paper are formed from a single folded-oversheet of paper, and the top and bottom layers 29T,29B of polyethyleneare formed from a single folded-over sheet of polyethylene, and thesqueeze-bonding occurs just at the left and right edges 25L,25R. Thismanner of forming the end of an envelope is depicted in the said U.S.Pat. No. 6,139,188, for example. Of course, folding the edge 24 requiressophisticated fold-making machinery.

As mentioned, the preferred application of the materials jointing systemdescribed herein is in making padded envelopes from polyethylenebubble-wrap and kraft paper. However, padded envelopes can be made fromother materials. For example, the polyethylene bubble-wrap may bereplaced with expanded polyethylene foam. Being polyethylene, suchexpanded foam material again is thermoplastic, and has a greatresistance to being punctured.

Many other plastic materials have the capacity to be heated beyond athermoplastic limit and to regain mechanical properties upon cooling,and have also the ability to become stretched rather than to puncture,when stressed by a sharp point, such a polypropylene, nylon, etc. Thesematerials may be considered for use in the invention, in which the mainrequirement is that un-punctured crowns of the thermoplastic filmmaterial can be pressed through punctured holes in the other material,and the crowns can then be heat-bonded to the punctured material.

Also, in the broad scope of the invention, the thermoplastic materialneed not be in bubble form, or expanded form, but may be in the form ofjust a single sheet or film.

The puncture-able material may be other than paper. The maincharacteristic required in this other material is that it be capable ofbeing punctured when pressed by a sharp point. The material may be afabric or cloth, for example; or the material may be a metal foil, forexample aluminum foil. Some speciality envelopes are made now usingcloth or aluminum foil.

As described above, a bubble envelope comprised layers of plainun-coated kraft paper and of bubble-wrap polyethylene. A stack of thelayers was joined at the marginal edges of the envelope by squeezing thestack between a pair of points-dies, which were formed with points thatpunctured the kraft paper but not the polyethylene. The points pushedcrowns of un-punctured polyethylene through the punctured holes in thepaper. Then, the marginal edges were squeezed flat between flat-dies,the flat-dies being heated enough to cause fuse-bonding. The margins ofthe finished envelope were held together not only by fuse-bonding, butby the presence of the polyethylene crowns, which, penetrating rightthrough the holes in the paper, serve as mechanical rivets. Thistechnique is termed the pierce-and-fuse technique.

It is recognised that the pierce-and-fuse technique, as disclosed in theprior patent application in respect of the bubble padded envelope, canbe utilised in respect of other packaging categories. In one example,the technique is used to join kraft paper to a planar film ofpolyethylene or other thermoplastic material, i.e to ordinary flatplastic film or sheeting, rather than to bubble material. This may beused to produce an envelope, or may be used in respect of objects ingeneral, in which sheets of various materials are joined together.

In general, the invention may be considered for joining two materialswhere (a) one of the materials has the characteristic that, when pressedby a point, the material is punctured, right through (like kraft, andmost kinds of paper); and (b) the other material has the characteristicthat, when pressed by the same point, the material stretches beyond itselastic limit, and yields, but is not punctured (like polyethylene andother plastics). The second material should be thermoplastic, i.e whenheated, and then cooled, the material loses its previous shape and takeson a new shape. With this combination of characteristics, and with someexperimentation as to temperatures, squeeze times, etc, satisfactoryjoints can be made in very many cases. The technique makes use of theapplication of heat, but the resulting bond is basically a mechanicalone. No adhesives or coatings are required.

In place of kraft paper, the technique may be used to join cardboard topolyethylene bubble, or flat film. Cardboard is more difficult to workwith, since its heat capacity is greater than paper, i.e cardboard takeslonger to heat up. Cardboard, and many other materials, and combinationsof materials, need careful control of temperature. There may be only afew degrees of margin between not hot enough (to fuse and seal thematerial) and being too hot (which causes burning).

With some materials, the piercing stage should be done with the piercingpoints-dies cold; with other materials, the points-dies may be, orshould be, hot. The designer should carry out experiments with theparticular materials, to determine what will be satisfactory in theparticular case.

When the piercing is done with points-dies that are hot, it may bepossible, with some materials, to combine the thermoplastic fusing stagewith the piercing stage, whereby the described subsequent separatehot-squeeze stage may be eliminated. In that case, of course theappearance of the bonded area will be different, in that, if the area ofthe joint is not hot-squeezed flat, the as-finished joint is left withthe form of the indentations caused by the points still present.

The designer should also experiment with the depth of penetration of thepoints. The penetration should be deep enough that the points prickright through the paper-like material, and leave the plastic material,not torn, but stretched. The penetration should-be just deep enough thatonly the tips of the points break through; where the one material isfibrous, it is preferred not to break or tear, but rather just toseparate, the fibres.

The pierce-and-fuse technique enables sheet polyethylene to be joined tothe very strong, synthetic fibrous smooth-finished material, which isused in some kinds of courier envelope. The material is known by the(Dupont) trade name Tyvek. Tyvek material can be glued to itself, toform seams, for the purposes of manufacturing the courier envelope. Butpolyethylene cannot practically be welded or bonded to Tyvek (nor tomany other materials) by the use of glue or adhesive. Only by theaddition of very expensive additives to the adhesives can polyethylenebe glued at all, to most paper-like materials, and the finish of Tyvekmakes it even less amenable. Also, as mentioned, in order to joinpolyethylene to paper or paper-like materials, it is sometimes preferredto pre-laminate a coating of polyethylene right into the paper; butagain, this is hardly practicable with Tyvek.

But still, it is very desirable to provide an inner bag of bubble,secured inside a courier envelope of Tyvek, and the pierce-and-fusetechnique enables this. The bag made of plastic bubble liner may beattached only at the marginal edges, and so is separable for re-cycling.The plastic liner bag may alternatively be done in plain polyethylenesheet or film.

As mentioned, the technique can be used to join sheet polyethylene tosheet cardboard. This is useful in the case of substances (includingfoodstuffs) that are commonly stored in plastic liner bags insidecardboard boxes. Fixing the plastic bag to the cardboard has been verydifficult, using traditional adhesives and like techniques.

When gluing food containers, the designer must make sure the adhesivesdo not release spurious chemical contaminants into the food. Acceptableadhesives for gluing cardboard food boxes, and acceptable adhesives forgluing plastic food bags, are readily available; but inexpensivepractical safe acceptable adhesives for gluing polyethylene to cardboardare not. However, the pierce-and-fuse technique is a mechanical, ratherthan an adhesive, jointing system; the technique does not tend tointroduce any chemicals that might be toxic in the context offoodstuffs.

The technique does not require that materials be pre-coated, and thetechnique can be used in cases where the material, for other functionalreasons, has a pre-coat of a material that is not compatible withpractical adhesives. Furthermore, adhesives usually require time to cureor set whereas the present technique the joint bond simply sets as itcools, as in welding.

The as-illustrated (FIG. 6) pyramid form on the points-dies isadvantageous from the standpoint that the multi-pyramid shapes can bemachined into the die-faces simply by running a suitably profiledgrinding wheel over the die-face. The pyramids thus produced have asharp point, and each pyramid also has four sharp side-edges. The sharppoint penetrates through the paper, but these sharp side-edges do notcut (i.e shear) through the paper; rather, the sharp side-edges may beregarded as creasing the paper and thereby concentrating the squeezingforce, as the dies are brought together, into a narrow line, andpressing the materials together in very intimate contact over thatnarrow line.

Thus, the pyramid form, in addition to providing the pierced points,also provides lines of intimate contact between the two materials,around the pierced points. This may be contrasted with, for example, theneedles-style of points-dies, as shown in FIGS. 10,11, which provideonly pierced points, but do not provide lines of intimate contact aroundthe pierced points. The presence of the lines of intimate contact may beexpected to enhance the security of the final fused joint.

The dies as described in the prior disclosure were flat-slab dies.However, it can be inconvenient to provide for the flat-slab dies toadvance in the direction in which the materials are being fed throughthe dies. Therefore, the bonding of the joints was done on a stop andstart basis. The materials were fed between the flat-slab dies and thenthe material stops while the dies are in actual operation. On the otherhand, using dies in the form of rollers allows the materials beingbonded to be fed through the rollers on a continuous basis; but it canbe difficult, using rollers, to hold a joint in a squeezed-togetherconfiguration, for longer than a moment.

Continuous throughput, without stopping and starting, is desirable, asis holding the joint together for a time period of several seconds.These conflicting functions can be met if the dies are arranged to moveon tracks, in which the dies are mounted on a flexible carrier having areturn. Alternatively, the dies can be solid, but mounted on a linkagewhich allows the die to travel along with the materials; then, uponbeing withdrawn from the joint area, the die can be returned by thelinkage.

As mentioned, the points should be arranged to penetrate right throughthe paper—and, when the items being joined are sandwiched between twosheets of paper, through both sheets of paper—to the extent thatpinpoints of light would be visible if the joint area were to be held upto the light. In fact, these pinpoints of light can serve as the basisfor an inspection technique. To do this, the pierced area is passedunder a light source, and a sensor determines the extent to which lightshines through. If the pinpoints are too small, or too large, or uneven,the machine can be stopped, and adjustments made. Or, the adjustmentscan be done automatically, responsively to the sensor signals. Often,the only adjustment required is in respect of the distance apart of thedies as they close together, or bottom out, and the extent to which thedies squeeze the sandwich is readily adjusted by the insertion ofappropriate die-closure shims.

As shown in FIGS. 12 a,12 b, the upper and lower points-dies have beenbrought together until the points just touch a stack 60 of sheets.Insofar as the sheets include bubble material, the bubbles arecollapsed, in the drawings, whereby the thickness H of the stack is theaggregate of the thicknesses of the material itself of each sheet. Thepoints-dies now lie a reference-distance S mm apart. In FIG. 12 b, thepoints-dies have been closed together, whereby now thematerial-thickness of the stack 60 is compressed between the dies, andof course, the sheets that make up the stack have been stretched overthe points. The points-dies now lie a distance C apart. Thus the dieshave moved together a distance S−C=M. The designer should arrange thedimensions of the points such that the distance M is about one mm.

The type of kraft paper used for bubble envelopes typically is 0.1 mmthick, and the polyethylene film from which the bubble is made typicallyis about 0.05 mm thick. It has been found that, with a stack of twosheets of kraft paper, and two sheets of bubble film, when the distanceM is about one mm, the points just break right through the paper, andalso cause the polyethylene of the bubble film to be stretched almostideally in the manner as shown in FIG. 8. The plastic film is stretchedbeyond its elastic limit, and takes a permanent set, as the crowns arepushed through the holes punctured in the paper. If the distance M weremore than about two mm, too much of the paper would be torn, which mightweaken the envelope; if M were less than about a half-mm, the pointswould not break through the paper reliably.

If the points were to be pushed too far through the paper, the papermight be weakened. Each of the punctured points in the paper preferablyshould be surrounded by a bridge of intact paper, forming a continuousring around the point. (This does not apply to the points at the veryedge of the paper, of course.) The continuous ring around each pointshould be nowhere less than one mm wide.

FIG. 13 is a plan view of a grid of points, where the grid spacingbetween adjacent points, as produced by one of the points-dies, is P mm.The points produced by upper points-die (the up-points) are shown asdots, whereas the points produced by the lower points-die (thedown-points) are shown as crosses. The up-points protrude downwards intothe paper, whereas the down-points protrude upwards out of the paper. Itwill be understood that the point-to-point spacing of the grid ofpoints, as a whole, now is P1. Assuming the dies (i.e the points) areaccurately identical, orthogonal, and symmetrical, the distance P1 isP.½√{square root over ( )}2 mm.

1. Procedure for attaching a sheet of puncturable-material to a sheet of stretchable-material, including: wherein the puncturable material is material that, upon being forcefully stretched over a point, is readily through-punctured, substantially without stretching; wherein the stretchable material is material that, upon being forcefully stretched over a point, readily stretches over the point, substantially without being through-punctured by the point; making a stack of sheets of puncturable material and stretchable material, in which the sheets lie in direct face-to-face touching contact with each other; providing a points-die; wherein a points-area of the points-die has many protruding points, which point towards the stack; wherein the points-area lies over, and thereby defines, an adherence-area of the stack; pressing and squeezing the points-die onto the adherence-area of the stack; then separating the stack from the points-die; and so configuring the points, and so squeezing the points-die onto the stack, that: at least some of the paints break through, and make holes right through, the puncturable material; and substantially none of the points breaks through, and makes holes right through, the stretchable material.
 2. Procedure of claim 1, wherein substantially all of the points break through, and make holes right through, the puncturable material.
 3. Procedure of claim 1, including so configuring the points, and so squeezing the points-die onto the stack, that, when the stack is squeezed by the points-die, crowns of the stretchable material become stretched over the points far enough for the stretchable material to be stretched beyond its elastic limit, and to take a permanent set.
 4. Procedure of claim 3, including: providing a flattening-die; after separating the stack from the points-die, placing the flattening-die against the adherence-area of the stack; squeezing the adherence-area of the stack with the flattening-die, in such manner as to flatten the adherence-area.
 5. Procedure of claim 1, wherein the puncturable material is characterised as a paper material, for example kraft paper.
 6. Procedure of claim 1, wherein the puncturable material is a light, strong, tear-resistant, synthetic-fibrous, smooth, paper-like material.
 7. Procedure of claim 1, wherein the stretchable material is characterised as a plastic film material, for example polyethylene film.
 8. Procedure of claim 1, wherein the stretchable material is bubble material, in which a base layer of plastic film material is adhered over part of its surface area to a bubble layer of plastic film material, leaving bubbles therebetween.
 9. Procedure of claim 1, wherein the stack is comprised of the following sheets of the materials; puncturable; stretchable; stretchable; puncturable.
 10. Procedure of claim 1, wherein the puncturable material is a metal foil material, for example aluminum foil.
 11. Procedure of claim 1, including providing an upper points-die and a lower points-die, wherein: the upper and lower points-dies have respective points-areas, which are co-extensive with the adherence-area of the stack; the points-area of the upper points-die has many protruding points, being the upper points, which are pitched on a grid a distance P mm apart; the points-area of the lower points-die has many protruding points, being the lower points, which are also pitched on a grid the said distance P mm apart; the upper points lie in a staggered relationship with respect to the lower points; the upper points fit into the spaces between the lower points when the points-dies are brought together; upon the points-dies being pressed and squeezed onto the adherence-area, up-points on the adherence-area produced by the upper points lie intercalated with down-points on the adherence-area produced by the lower points; whereby the up-points and the down-points, on the adherence-area of the stack, together lie pitched on a grid a distance P.½√2 mm apart.
 12. Procedure of claim 11, wherein the configuration of the points-dies is such that: the points-dies have a slack-take-up separation, being S mm, being the separation of the points-surfaces at which a flat layer of material having a thickness of H mm lies between, and just touching, the upper and lower points-surfaces, without the material of the layer being stretched over the points; the points-dies have a closed-together separation, being C mm, being the separation of the points-surfaces at which the dies lie closed together onto the flat layer of thickness H mm; and the distance the points-dies move together, in going from a separation of S mm to a separation of C mm, being S−C, is M mm; and M mm is between ½ mm and 2 mm.
 13. Procedure of claim 11, wherein the points are pitched a distance P apart, P being the closest distance between adjacent points, where P is between 1½ mm and 5 mm.
 14. Procedure of claim 11, wherein the points are provided on the points-surface of the points-die as pointed pyramids.
 15. Procedure of claim 14, wherein the pyramids are regularly-pitched, on a grid in which the pyramids are pitched a distance P apart, where P is between 1½ mm and 5 mm.
 16. Procedure of claim 11, including the following procedure for manufacturing the points-dies: passing a cutting wheel, having a V-shaped cutting profile, in such manner as to form V-shaped grooves, over the points-die in a first direction, and passing a cutting wheel, having a V-shaped cutting profile, over the die in a second direction: wherein the second direction is orthogonal to the first direction; and making the grooves deep enough that pointed pyramids are left between the grooves.
 17. Procedure of claim 16, wherein the V-shaped profile has an included angle of between 90 degrees and 60 degrees.
 18. Procedure of claim 1, wherein: the puncturable material is characterised as a paper material, for example kraft paper; the stretchable material is bubble material, in which a base layer of plastic film material is adhered over part of its surface area to a bubble layer of plastic film material, leaving bubbles therebetween; the stretchable material is bubble material, in which a base layer of plastic film material is adhered over part of its surface area to a bubble layer of plastic film material, leaving bubbles therebetween; and the stack is comprised of the following sheets of the materials: paper; bubble; bubble; paper.
 19. A padded bubble envelope that has been manufactured by the procedure of claim 18, in which the adherence-area is free of glue or adhesive.
 20. Procedure for attaching a sheet of puncturable-material to a sheet of stretchable-material, including: wherein the puncturable material is material that, upon being forcefully stretched over a point, is readily through-punctured, substantially without stretching; wherein the stretchable material is material that, upon being forcefully stretched over a point, readily stretches over the point, substantially wIthout being through-punctured by the point; making a stack of sheets of puncturable material and stretchable material, in which the sheets lie in direct face-to-face touching contact with each other; providing a points-die; wherein a points-area of the points-die has many protruding points, which point towards the stack; wherein the points-area lies over, and thereby defines, an adherence-area of the stack; pressing and squeezing the points-die onto the adherence-area of the stack; then separating the stack from the points-die; and pressing the points-die hard enough to puncture the puncturable-material immediately over the points, but lightly enough to leave a bridge of the puncturable material still intact, between the points.
 21. Procedure of claim 20, including: wherein some of the points are edge-points, being those points in respect of which no other one of the points lies nearer to an edge of the stack; pressing the points-die onto the stack in such manner that, upon the stack being separated from the points-die, in respect of each of the points that is not an edge-point, there remains a bridge of intact material between adjacent points; and the bridge forms a continuous ring around each one of the points.
 22. Procedure of claim 21, wherein, in respect of each point, the continuous ring is nowhere less than 1 mm wide.
 23. Procedure for attaching a sheet of puncturable-material to a sheet of stretchable-material, including: wherein the puncturable material is material that, upon being forcefully stretched over a point, is readily through-punctured, substantially without stretching; wherein the stretchable material is material that, upon being forcefully stretched over a point, readily stretches over the point substantially without being through-punctured by the point; making a stack of sheets of puncturable material and stretchable material, in which the sheets lie in direct face-to-face touching contact with each other; providing a points-die; wherein a points-area of the points-die has many protruding points, which point towards the stack; wherein the points-area lies over, and thereby defines, an adherence-area of the stack; pressing and squeezing the points-die onto the adherence-area of the stack; then separating the stack from the points-die; providing an upper points-die and a lower points-die, wherein: the upper and lower points-dies have respective points-areas, which are co-extensive with the adherence-area of the stack; the points-area of the upper points-die has many protruding points, being the upper points, which are pitched on a grid a distance P mm apart; the points-area of the lower points-die has many protruding points, being the lower points, which are also pitched on a grid the said distance p mm apart; the upper points lie in a staggered relationship with respect to the lower points; the upper points fit into the spaces between the lower points when the points-dies are brought together; upon the points-dies being pressed and squeezed onto the adherence-area, up-points on the adherence-area produced by the upper points lie intercalated with down-points on the adherence-area produced by the lower points; whereby the up-points and the down-points, on the adherence-area of the stack, together lie pitched on a grid a distance P.½√2 mm apart; after the points-dies have been pressed and squeezed onto the adherence-area, the puncturable material remains intact, and not punctured, over a bridge portion of +the puncturable material, between the up-points and the down-points; and the un-punctured bridge portion is at least 1 mm wide.
 24. Procedure for attaching a sheet of puncturable-material to a sheet of stretchable-material, including: wherein the puncturable material is material that, upon being forcefully stretched over a point, is readily through-punctured, substantially without stretching; wherein the stretchable material is material that, upon being forcefully stretched over a point, readily stretches over the point, substantially without being through-punctured by the point; making a stack of sheets of puncturable material and stretchable material, in which the sheets lie in direct face-to-face touching contact with each other; providing a points-die; wherein a points-area of the points-die has many protruding points, which point towards the stack; wherein the points-area lies over, and thereby defines, an adherence-area of the stack; pressing and squeezing the points-die onto the adherence-area of the stack; providing a flattening-die; after separating the stack from the points-die, placing the flattening-die against the adherence-area of the stack; squeezing the adherence-area of the stack with the flattening-die, in such manner as to flatten the adherence-area.
 25. Procedure of claim 24, including: providing the stretchable-material as a thermoplastic material, having a thermoplastic temperature threshold; heating the material above the said threshold; while the material remains above the said threshold, squeezing the adherence-area of the stack with the flattening-die; then separating the stack from the flattening-die, and allowing the material to cool.
 26. Procedure for attaching a sheet of puncturable-material to a sheet of stretchable-material, including: wherein the puncturable material is material that, upon being forcefully stretched over a point, is readily through-punctured, substantially without stretching; wherein the stretchable material is material that, upon being forcefully stretched over a point, readily stretches over the point, substantially without being through-punctured by the point; making a stack of sheets of puncturable material and stretchable material, in which the sheets lie in direct face-to-face touching contact with each other; providing a points-die; wherein a points-area of the points-die has many protruding points, which point towards the stack; wherein the points-area lies over, and thereby defines, an adherence-area of the stack; pressing and squeezing the points-die onto the adherence-area of the stack; then separating the stack from the points-die; and wherein: the stack is comprised of the following sheets of the materials: puncturable; stretchable; stretchable; puncturable; the sheets of material are arranged in the stack so as to form the front and back of an envelope, having left and right edges and a bottom edge, which are closed, and having a top edge, which is open, and which includes a fastener for closing the envelope; the adherence-area is a relatively-narrow continuous marginal area, contiguous with the left, right, and bottom edges; the procedure is carried out in such manner as to ensure that, over at least a major proportion of the total area of the stack of sheets, the sheets are not adhered together.
 27. An envelope that has been manufactured by the procedure of claim
 26. 